This invention relates to mechanical rotary vacuum pumps and, more particularly to improvements in the rotors of such pumps.
Rotary vacuum pumps of the type having a rotor mounted for rotation in a stator body and being offset in relation to the stator bore such that two blades contained in, and slidable within, diametrically opposed slots in the rotor can cause gas entering the space between the stator and the rotor to be compressed and expelled into a pump outlet.
A typical arrangement in known pumps is shown schematically in FIG. 1 in the form of four vertical sections through the pump at four different phases thereof (induction, isolation, compressed and exhaust). There is shown a stator body 1 having a substantially cylindrical bore within which is eccentrically mounted a rotor 2 for rotation therein about its center line.
The rotor has two diametrically opposed slots within which are situated two blades 3,4 which can slide radially within the slots and are urged outwardly by means of a spring 5 such that the tips 6,7 of the blades 3,4 respectively are in contact with the stator wall at all times.
The stator body 1 has an inlet 8 to the bore and an outlet 9 therefrom, the outlet 9 also having a one-way exhaust valve 10.
The mechanism is generally lubricated by oil 11 contained in the pump body 12 in the form of a reservoir, small amounts of which are pumped into the pump interior to form a thin oil film between the working components before being ejected back into the reservoir through the exhaust valve 10 together with the pumped gas.
The rotor component itself is of complex design and construction in order to accommodate the two sprang blades. It commonly comprises an assembly as shown in FIG. 2--a sectional view through the assembly--and in FIG. 3--a separate sectional view along the line III--III of FIG. 2--having two half-cylindrical portions 20,21 defining therebetween one substantially continuous slot 22 for receiving two blades 23,24 of substantially rectangular shape and of a thickness very slightly less than that of the slot itself.
To hold the portions 20,21 together and to enable the rotor to be mounted for rotation in the pump body, boss elements 25,26 commonly formed integrally with shaft portions 27 and 28,29 respectively and all of cylindrical cross section are joined to the portions 20,21. Bearing and shaft seal surfaces are provided by the shaft portions 27 and 29.
The complete rotor assembly is then mounted within pump body bearings for rotation therein by means of a motor in the usual way. It will be appreciated, however, that the construction of such a known rotor assembly is complicated and therefore expensive.